1. Field of the Invention
This invention relates generally to a novel class of functional copolymers and derivatives thereof which can be used as aminoplast crosslinking agents in a variety of fields, and particularly in the coating field.
2. Description of the Related Art
To effectively crosslink with a variety of widely available difunctional materials such as diols, dicarboxylic acids, dimercaptans, and diamides, a monomeric crosslinking agent is required to have a functionality effective for crosslinking of greater than two, and preferably at least 3. In many cases, however, even trifunctional aminoplast crosslinking agents do not give rise to sufficient crosslinking density in cured films or objects due to incomplete reaction of the functional groups, and as a result, cured films with inferior physical and resistance properties are obtained.
The problem of insufficient crosslinking density may be overcome by using a higher functional aminoplast crosslinker such as hexamethoxymethyl melamine. In these cases, however, the films obtained sometimes have low flexibility due to the somewhat rigid network produced in the films upon cure.
The above-identified problems of insufficient crosslinking of the low functionality crosslinkers and the low flexibility of the highly functional crosslinkers may be overcome by using typically tetrafunctional guanamine-derived aminoplast crosslinking agents. However, guanamine-derived crosslinkers are more difficult and more costly to prepare than melamine-derived crosslinkers. Furthermore, some guanamine crosslinkers such as N,N,N',N'-tetraalkoxymethylbenzoguanamines may have insufficient resistance properties for certain applications, and generally have inferior stability towards the degradative action of ultraviolet light.
The present invention, therefore, provides new polyfunctional, amino resin derived, copolymeric crosslinking agents which are capable of self crosslinking or crosslinking with active hydrogen containing materials thereby producing, upon cure, films which have good acid resistance properties, environmental etch resistance, and a good balance of hardness and flexibility.